Treating fluid mixtures



y 1944- B. 1. SMITH ET AL TREATING FLUID MIXTURES t ulm \on wn II... I uv WN Q wk (wt 2 Sheets-Sheet -1 Filed Jan. 2, 1941 May 9, 1944. B. 1.SMITH ETAL 'TREATIING FLUID MIXTURES Filed Jan. 2, 1941 2 She etsSheet 2M w 8% ma uNm w MNN wNN m mm m: N @N stituents.

' Patented May 9, 1944 TREATING FLUID MIXTURES. Brook 1. Smith, andEdward G. Morin, Elizabeth,

1., asslgnors to Standard Oil Development Company, a corporation ofDelaware Application .lanuary2, 1941, Serial No. 372,854

16 Claims. (or. ez-orss j This invention relates to the separation ofhydrocarbofi mixtures into desired fractions and more particularlyrelates to a process for. separating reaction products into desiredhydrocarbon cuts having difierent molecular weights such as C2, C3, C4,etc. fractions. m In the cracking of hydrocarbon oil, if a relativelyhiglr temperature and steam are used, the reaction products or productsof conversion contain olefins and aromatic constituents. This inventionis especially adapted for separating ole fins such as ethylene andotherhydrocarbons from the reaction products resulting from conversion ofhydrocarbons. However, the invention is adapted for use in separatingdesired fractions from mixtures of hydrocarbon gases.

The products of conversion are cooled, the

water removed and the normally liquid hydro-- carbons and thehydrocarbon gases are compr ssed and cooled as separate streams and arethen passed into a last drum wherein liquids are separated from gases.Theseparated liquid is passed to a iractionatlng tower to remove C4 andlighter hydrocarbons from an aromatic fraction containing gasolineconstituents which is withdrawn from the bottom of the fractionatingtower. The vapors separated in the last drum, above-mentioned, are mixedwith the separated Cd and lighter hydrocarbons leaving the fractionatingtower. the mixture is cooled and passedto a separator to separatecondensed liquid from vapors and gases. The separated liquid is returnedto the drum above referred to.

The vapors and'gases are dehydrated or dried, compressed, cooled andfractionated in a first fractionating tower to separate the lighterconstituents as overhead vapors from heavier constituents. This fractionis a dilute ethylene fraction and contains ethylene, methane andhydrogen. The bottoms from the first fractionator are passed to a secondfractionator in which the bottoms are fractionated Reirigeration is usedfor providing reflux for nantly propylene.

the first two fractionating towers described above and for condensing aportion of the feed to the first tower. A C: out is used as therefrigerant with a portion of the overhead fracit is passed to thedehydrators or driers.

The dilute ethylene fraction is preferably used for cooling theliquefied propylene before the.

dilute ethylene fraction is removed from the system.

The dehydrators become inactivated after being in use for a certainperiod or time and they are revivifled by passing hot natural gastherethrough. However, regeneration of the dehydrators may beaccomplished by the use of other hot gas streams at the propertemperature. After the dehydrators have been dried and before puttingthem on stream, a portion of the cold dilute ethylene traction may bepassed through the dehydrators for cooling them to the propertemperature.

In the drawings there is shown in Figures 1 and 1A a diagrammaticrepresentation for one form of apparatus adapted for carrying out theprocess of this invention but the invention is not to be restrictedthereto as other forms of apparatus may be used. Figure 1A forms a comtinuation of Figure 1.

Referring now to the drawings, the reference character it designates aline through which a relatively heavy oil such as gas oil, reducedcrude, or the like, is passed by means of pump it. The oil is fedthrough a heating coil ,Ilt in. a furnace it for heating the oil to atemperature below cracking but sumcient to substantially completelyvaporize the oil. The heated and vaporized oil is passed through line itand into a separating tower 22. superheated steam is preferably added tothe hydrocarbon oil during heating in the coil M as at 23. Thevaporizing furnace it is shown in greater detail in the case filedconcurrently herewith in the names of Brook 1. Smith and John E. Donahueand bearing Serial No. 372,855.

' In the separator 32 unvaporized constituents are separated from vaporsand withdrawn from the bottom thereof through line it. The vapors arefractionated in the separator 22 and'preferably suitable reflux isintroduced into the top of the separating tower 22 through line 28. The

vapors passing overhead are at atemperature The products of conversionare passed through line 86, are quenched by the introduction of a quenchoil through line 88 and the quenched products below a crackingtemperature are introduced into a separating and fractionating tower atto separate liquid residue from vapors in the lower portion 43 of thetower '82. The liquid residue is withdrawn from the bottom of theseparator 43 through line 44.

The separated vapors are fractionated in the fractionating section d5 ofthe tower 52 to separate condensate oil from lighter constituents. Thelighter constituents pass overhead as vapors through line 68 and arefurther treated as will be presently described. Preferably refiuxisintroduced into the fractionating section 53 through line d8. Condensateoil collecting on the trap-out tray 82 is preferably withdrawn therefromthrough line at. The overhead vapors in line 58 contain ethylene,methane, hydrogen, steam, Ca, Ca and heavier hydrocarbons. One exampleof a hydrocarbon mixture to be separated is as follows:

Composition of product from furnace in line 36 M01. Percent 34.7

The steam cracking of a relatively heavy hydrocarbon oil at elevatedtemperatures forms the subject matter of another application filedconcurrently herewith in the name of Brook I. Smith Serial No. 372,853.The showing is included in this case in order to illustrate a completeprocess, As disclosed in the other application, the condensate oilwithdrawn through line 54 is preferably used as reflux in towers 22 and42 and ,as quench through line 88.

The fractionating section 85 is under a pressure of about '7 pounds persquare inch'and thevapors passing overhead through line 40 are at atemperature of about 230 F. These vapors are cooled by passing through acondenser 88 to condense water and normally liquid hydrocarbons andthe'cooled and condensed constituents are introduced into a separatingdrum 58. The condensed water settles as a bottom layer in the drum 58and is withdrawn through a water draw-off pot 62. The condensedhydrocarbons form an upper layer on the water and are withdrawn throughline 64. The uncondensed hyasaaeso drocarbons leave thev top of the drum5!. as apors through line 68 and are introduced into a knock-out drum 88for separating any entrained liquid from the vapors.

Any separated liquid is withdrawn from the bottom of the drum 68 throughline 12 and mixed with the liquid withdrawn from separating drum 58through line 84. The knock-out drum 88 is under a pressure of about 2pounds per square inch and at a temperature of about 110 F. The vaporspass overhead from drum 68, through line it and are compressed bycompressor I6 and cooled in a cooler F8. The cooled and compressedvapors are passed through line 82 and into an inter-stage knock-out drum88 which is under a pressure of about 40 pounds per square inch and at atemperature of about 120 F. Introduced into the drum 88 is thehydrocarbon liquid withdrawn from the first drum 58, the liquid beingpassed through line M by means of pump 81.

In the intermediate drum 86 there is a separation of water, liquidhydrocarbons and vapors and gases. In the compression and cooling of thegases passing through line I4 additional quantitles of hydrocarbons andwater are condensed. The water is withdrawn as a bottom layer throughline 88. The liquid hydrocarbons form an upper layer on the water andare withdrawn through line 82. i

The uncondensed hydroca*"ons leave the top of the intermediate drum 86-.means of line 84.

These vapors are compressed in passing through compressor 88 and arethen cooled and partly condensed in a cooler 88. The cooled andcompressed vapors and gases are passed through line 502 where they aremixed with liquid withdrawn from the intermediate drum 88' and passedthrough line 92 by means of pump I04. The mixture of gases, vapors andliquid is introduced into a last drum I08 which is under a pressure ofabout 175 pounds per square inch and at a temperature of about 120 F.

During cooling of the compressed gas passing through line 94, there isfurther condensation of water and hydrocarbons which accumulate asseparate layers in the last drum I08. The water is withdrawn from thebottom of the drum through line H2. The liquid hydrocarbons arewithdrawn through line II4 from the drum I08.

The uncondensed hydrocarbons comprising vapors and gases are passedoverhead through line H6 and are further treated as will be described ingreater detail hereinafter.

The liquid hydrocarbons are withdrawn from the drum I08 by means of pumpH8 and passed through a heat exchanger I22 for preheating the liquidhydrocarbons. The preheated hydrocarbons are then-passed through lineI23 to a fractionating tower I24 for separating normally liquidhydrocarbons from C4 and lighter hydrocarbons. The fractionatingtowerI24 may be called a debutanizing tower. The tower I24 is maintainedunder a pressure of about pounds per square inch. 7

Heat is supplied to the bottom of the tower for scribed.

This condensate oil comprises a relatively heavy.

aromatic fraction containing gasoline constituents and containingsubstantial amounts of henzene, toluene, xylene and higher aromaticcompounds. The aromatic fraction is further cooled by passing throughthe cooler I38 and is then passed through line I42 to a storage tank orthe like Mil for the relatively heavy aromatic fraction.

The uncondensed vapors leave the top or the fractlonating tower I24through line I46 at, a temperature of about 163 F. The vapors are passedthrough a condenser I48 and then to a separator I52 for separatingliquids from vapors. The liquids are withdrawn from the bottom of theseparator I52 through line I54 and returned to the top of the tower 524as reflux by'means of pump 556.

The separated vapors leave the top 01' the separator 52 through line I58and are combined with the uncondensed vapors leaving the top of the lastdrum I08 above described and this mixture is iurther treated as will bepresently de- From the above, it will be seen that only the liquidhydrocarbons from the last drum I08 are passed to the fractionatingtower I24 and the separated vapors from the drum I88 are not passedthrough the fractionating tower I24 but are mixed with the vaporsresulting from the The mixture is preferable passed through a scrubberltd where it is scrubbed with caustic soda or any other suitable reagentfor the removal of sulfur compounds and the scrubbed vapors and gasesare then passed through line lot, cooled first by passing through thecooler E66 and then by indirect contact with cold propylene gas or byevaporation of liquid propylene in exchanger I68.

By this refrigeration, some oi the heavier hydrothe separator I52 hasabout the following composition:

' Moi. percent Hr 7.2 GHc 24.8 CzH i. 25.8 CaHc 10.3 CsHc 16.5 cent 2.3time 2.6 CtHs 6.6 (EH10 Ml Ca5+ 2.9

carbons may be condensed and the refrigerated vapbrs are passed throughline I12 and introduced into a separating drum in .i'or separatingcondensed hydrocarbons irom vapors. The vapors introduced into theseparating drum I14 are under a pressure of about 170 pounds per squareinch and at a temperature of about F. The separated liquid hydrocarbonsare withdrawn from the bottom of the drum I14 and passed through lineI18 by pump I11 and returned to the last drum I88 which is at a highertemperature and lighter constituents are removed from the liquidhydrocarbons.

The separated vapors leave the separating drum I14 through line I18 andare passed through line I80. open valve I99 and into the first drier ordehydrator I82 which contains a suitable dehydrating agent such asactivated alumina I83. It is necessary to remove substantially all ofthe water vapor from the gases being treated in this process due to therelatively low temperatures used in the subsequent fractionation steps.If the water vapor were not removed, ice or hydrates would be formed inthe cold parts of the equipment and the lines would clog up and it wouldbe necessary to stop the process to remove ice formations.

Another drier dehydrator I88 is shown. Any number of dehydrators may beused. While one dehydrator is being use, another or other dehydratorsare being revivified to prepare them for the use in the process. whenthe dehydrator I82 is being used, the remaining valves are closed toprevent hydrocarbon vapors from line I18 frompassing through the otherdehydrator.

The dehydrated vapors leave the dehydrator I82 through. line I92, thevalve I98 being open.

The refrigerated compressed charge is introduced into a firstfractionating tower 282 which is under a pressure or about 575 poundsper square inch. The introduced hydrocarbons are fractionated in thetower 202 to separate lighter hydrocarbons from heavier hydrocarbons.The iractionating tower 202 is provided with a top bubble cap plate 2M1upon which liquid collects as shown at 206. Dripping under the surfaceof the liquid 2M3 is a pipe tilt which is associated with a higher platetit which is not a bubble plate upon which liquid accumulates as shownat hit. The liquid did comprises a seal for the pipe N8. Uncondensedvapors are withdrawn from the space above the top plate 2M by means ofline 2 i t and passed through a refrigerated cooler or refrigerationzone lit to reduce the temperature of the vapors to about 5i) F. Therefrigreflux. The liquefied constituents accumulate on sealing plate W2and excess quantities thereof are drained from plate 2I2 by means oftube 20$.

4= asaaeae The uncondensed vapors leave the tone! the tower 202 from thespace above the liquid shown at 2M and are passed through line 22d.These uncondensed gases contain ethylene, methane and hydrogen. andcomprise a dilute ethylene fraction which may be used as such withoutfurther treatment in the preparation of organic compounds such as ethylchloride, etc This dilute ethylene fraction has about the followingcomposition:

Moi. per cent Hi! 15.0 CH4 7 51.0 ("one Pa e 1% This dilute ethylenefraction is at a very low temperature and is preferably used for coolingpurposes before it is utilized in the manufacture of other compounds.The steps of cooling with this dilute ethylene fraction will bedescribed later in the process.

The condensate from the bottom of the first tower 222 is withdrawnthrough line 226 and passed into a reboiler 228 wherein its isindirectly heated by means of steam passing through vaporizing thehydrocarbons and the hydrocarbon vapors are fractionated as they passupwardly through the tower 262.

gases are withdrawn from the top of the fractlonating' tower 242 throughline 282. This fraction contains mostly ethylene and may be described asa. concentrated ethylene fraction hav- The condensate liquid iswithdrawn from the bottom of the tower 2G2 through line 252 and- Pal-TA2 1 (qt-r 24 5 CaHs 65.5 Cal-Tn 7.4

mg tower 258 wherein further fractionation is effected as will bepresently described.

Returning now to the-lighter constituents passing overhead from thesecond fractionatins tower 242 it will be" seen that the upper portionof the tower 242 is of a construction similar to that shown in the firstfractionating tower 202. A

The tubular certain of the relatively higher molecular weighthydrocarbons in the vapors are condensed. The refrigerated mixturecontains liquefied hydrocaring about the following composition:

Moi. per cent CHO 1.9

(ai le 90.0 (MT-in. 7.1 C'IHG 1.0

This fraction may be used as a starting prodnot for the manufacture oforganic chemicals such as ethyl chloride, etc.

The condensate liquid introduced into the third iractionating tower 258is under a pressure of about 230 pounds per square inch and heat issupplied to the bottom of the tower to vaporize the hydrocarbons and toremove lower molecular weight hydrocarbons overhead. Fractionated vaporsleave the top of the tower 258 through line 28s, are cooled andcondensed by being passed through condenser 28B and the cooled andcondensed vapors are passed through line 288 into a receiving drum 292.A portion of the liquid is withdrawn from the bottom of the drum 292 andreturned to the top of the tower 258 as reflux through line 294 by pump296. The remaining low boiling or lower molecular weight hydrocarbonscollecting in the drum 292 are withdrawn as vapors overhead through line298 and a portion thereof is removed as a 0i fraction, the rest beingadded to replace refrigerant lost in the refrigeration system which willbe described hereinafter in greater detail. In this way waterfreerefrigerant is added to the refrigeration system. The fraction separatedas the overhead fraction from th tower 258 comprises a Ca out havingabout the following composition:

M01. per cent The separated fraction comprising Ca hydro- -carbons ispassed through a condenser 289 and under a pressure of about 320 poundsper square inch and at a temperature of about 95 F. is introduced intoan accumulator or the like 800. The C: out under pressure is withdrawnfrom the tank 300 by means of line 3M and forms a part oftherefrigeratlon system later to be described.

Most of the Ca fraction is removed from the system through line 302 bypump 304. This fraction may be used in any desired manner for themanufacture of other compounds but is particularly adapted forpolymerization units. If it is so desired the Ca cut may. be withdrawnfrom the system as a gas by passing from line 288 to line 306' to apolymerization plant or thelike.

It will be seen that the C: out. contains a relatively large amount ofethane, namely, about 24.5 mol. percent and due to the presence ofethane in .the mixture, lower refrigeration temperatures are obtainedfor the same pressure than where a relaassaoso I cooling is obtainedwith this particular fraction recovered from the system. 1

The condensate liquid from the bottom of the fractionating tower 258 ispassed through lin 305 into a rebciler 306 which is indirectly heated bymeans of live steam passing through coil 301. vaporized constituentspass overhead through line 308 at a temperature of about 218 F. and arereturned to the bottom oi the tower 258. The unvaporized condensate oilis withdrawn from the reboiler 3M and passed through line 3l2 having apressure reducing valve 3 l 4 into the iractionating tower its.

The last fractionatin'g tower 386 is provided with heating means at thebottom thereof for heating and vaporizing the hydrocarbons introducedinto the tower 316. The fractionated vapors leave the top of the tower386 through line hit, are cooled and condensed bypassing throughcondenser 322 and are introduced into the seporator 324 by means of line326. Liquid accumulating in the separator 024 is withdrawn from thebottom thereof through line 323' and passed to CaHs 7.6 UZiHit 4.7 Cam21.4 Com 57.6 (Anni 7,7 Co 1.6

This Ce traction contains some butadiene which is preferably removedfrom the C4 fraction. The Cc fraction free of butadiene may be treatedin any suitable manner to produce desired hydrocarbons. Theiracticnating tower 3% is under a pressure of about $5 pounds per squareinch.

The condensate liquid remaining after fractionation is withdrawn fromthe bottom of the tower 3th through line see and passed into a reboilerW8 which is indirectly heated by live steam introduced into a coil 382.some of the lower molecular weight hydrocarbons are vaporized irom. thecondensate liquid and are introduced into the bottom portion of thetower SIS through line 3. The unvaporized condensate liquid is withdrawnfrom the reboiler 338 by means of line 3M and comprises a light aromaticfraction containing gasoline constituents and containing substantialamounts of benzene, toluene, xylene. and higher aromatics. Thisaromaticfraction may be used as such but it is preferably blended withthe aromatic fraction withdrawn from the bottom of the debutanizer towerI24 and stored in tank I.

The refrigeration system will now be described. The C: fractioncontaining liquefied ethane, pro pane and propylene under 'a pressure ofabout 320 pounds per square inch and at a relatively low temperature ofabout 95 F. is withdrawn from the tank 300 and passed through line 3M bymeans of pump 352. The C3 fraction is passed through a cooler 354through which water is passed by means of a coil 353 to reduce thetemperature of the C3 fraction. In order to further cool the C:fraction, it is passed through a heat exchanger 358 wherein'it isindirectly contacted with the dilute, cold ethylene traction passinthrough line 224 as above described. The Ca fraction leaving the heatexchanger 356 is at a temperature 0! about 65 F.

This C4 fraction has The 0: fraction is now used for refrigeratingcertain portions of the fractionation system. One portion of the C:fraction is passed through line 358 having a pressure reducing valve 362and then through refrigerating zone 216 for cooling the overhead gasesfrom the fractionating tower 242 from which concentrated ethylene istaken overhead. Due tothe pressure reducing valve 362, the v pressure onthe Ca fraction is reduced to about 5% pounds per square inch absolutewith a consequent reduction in temperature to about --2 F. The C3 cut iscooled to this temperature by the vaporization of a portion of the C3cut. The liquid and gaseous C: out at a temperature of about -2 F.enters the refrigeration zone 216. Vapors from fractionating tower 242enter the refrigeration zone 216 through line 214 andare cooled byevaporation of the liquid portion of the Ca cut. The vaporized Caconstituents are then passed through line 363 and are recompressed andcooled as will be presently described.

Another portion of the liquefied C3 fraction is passed through line 384having a pressure reducing valve 366 and the vaporized Cs constitumtspass through the refrigeration zone I98 for chilling the dehydrated andcompressed fraction being introduced into the first fractionating tower292 from the top of which a dilute ethylene fraction is recovered. Thevaporized Ca constituents are then passed through line 368 and mixedwith the vaporized C3 constitluents passing through line 363, themixture being passed through line 3'12 to an intermediate drum 216 undera pressure of about 53 pounds per square inch absolute before beingrecompressed as will be presently described.

Another portion of the liquefied C3 constituents is passed through line376 having a pressure reducing valve 318 and through the refri erationzone 2i 8 which is arranged above the first fractionating tower 202 fromwhich the lighter constituents are withdrawn overhead as a diluteethylene traction. Due to the pressure reduction, the C3 constituentsare vaporized in the refrigeration zone 2l8 to cool the gases passingtherethrough in line 2|6 and the vaporized Ca constituentsleave therefrigeration zone 2 I8 at a temperature of about F. Due

' to this low temperature, the Ca constituents are tion zonesabove-described.

preferably used in an additional cooling stage. The C: vapors from therefrigeration zone 2! 8 are passed through line 382 and through therefrigeration zone I68 wherein they indirectly contact vapors beingpassed to the separator I'll ahead of the dehydrators I82 and I88.

In obtaining the low temperature required for the refrigeration zone 2|8, it was necessary to reduce the pressure to a low figure. The pressureon the Ca constituents leaving the refrigeration zone 2 i0 is much lowerthan the pressureon the refrigerant leaving the other refrigera- Therefrigerant at the low pressure is passed through line 384 to a drum 386under arpressure of about 9 pounds per square inch absolute. The C;vapors are withdrawn from the drum 388 and compressed pressed to apressure of about 325' pounds per square inch and introduced into athird drum 3%. From the drum 898, the compressed C:

' constituents are passed through line 39s, are

mixed with the Ca fraction separated from the gaseous mixture beingfractionated and passing through line 298, the mixture being passedthrough the cooler 298 before being introduced into the tank and.

Returning now to the dehydrating or drying system. After the dehydratorit? has been in service for a certain length of time, it will becomeinactivated due to the adsorption of water vapor from the'gases beingdehydrated. When.

' dehydrator 688. A heated fluid is then passed through the dehydratorits to remove moisture from the alumina therein. Heferably natural gasis used but other hydrocarbon mixturemor other gases or agents may beused. The hydrocarbon gas is preferably passed through a coil in thevaporizing furnace it (through lines not shown) and heated to atemperature of about 600 F. and then passed through line 606, open valvesot, dehydrator m2, and line Md having the valve did open. The dryinggas is then passed through line M8, cooler 622 and then passed throughline 6% for use as fuel or for any other desired purpose. 7

After the alumina in dehydrator 582 is reactivated, the flow of. heatedgas therethrough may be stopped. The dehydrator is then at a relativelyhigh temperature and it is preferablycooled by by-passing a portion orall of the cold dilute ethylene fraction from line 2% through line 4526having a valve 429 and also preferably a strainer (not shown). The colddilute ethylone fraction is then passed through line 632, open valve434, then through the dehydrator it, then through line 83d having avalve M2 and then through line B. cooler s2: and then through line 424from which the dilute ethylene fraction is removed through line 444.When the dehydrator i8! is sufilciently cool. the flow of the colddilute ethylene fraction therethrough is stopped and the dehydrator isthen ready for reuse. V

The other dehydrator I88 is similarly treated to reactivate the aluminaand to cool the alumina after it has been dried. with valve 408 closed,the heated hydrocarbon drying gas is passed through line 588, open valve668, dehydrator H88, valve 1 and line 8 and then through line 8, cooler522 and outlet line Mil.

After the alumina in dehydrator its is dried, the new of hot hydrocarbongas is stopped and the cold dilute ethylene fraction or a portionthereof is passed through line 832 and with valve 434 closed, the diluteethylene fraction passes through open valve 9 through the dehydrator I88and then through open valve 852 in line Q56 and then through line 408,cooler 22 and outlet line 4. Instead of using the cold ethylenefraction, other refrigerants or cooling means may be used to cool thedehydrators.

While the process is especially adapted for separating desired fractionsfrom cracked products, the process is also adapted for separatinggaseous hydrocarbon mixtures into desired frac- 7 assaeso scribed. Theconditions given above in the de-' scription pertain to one gaseousmixture as an example but it is to be understood that the conditions maybe varied with different gaseous mixtures or similar gaseous mixtureswithout departing from the spirit of the invention.

In the abovedescription where pressures are referred to, the pressuresare given in pounds per square inch gauge unless otherwise specified.

By making a rough separation in the tower 20! allowing about one half ofthe ethylene to be removed wlth the overhead fraction and the remainderof the ethylene to pass from tower 202 in. the bottoms fractioncontaining C2 and heavier hydrocarbons, it is possible to remove methaneand hydrogen from C: and heavier hydrocarbons at a higher temperaturelevel and with less refrigerated cooling required. With the methone andhydrogen removed from the remaining ethylene and heavier hydrocarbons,the remaining ethylene can be recovered in relatively concentrated formas an overhead fraction from tower 262.

While one form of apparatus has been disclosed for carrying out thefractionation process, it is to be understood that this apparatus is byway of example only and various changes and modifications may be madewithout departing from the spirit of the invention.

What is claimed is:

1. a method of separating lower molecular weight normally gaseoushydrocarbons from mix tures containing them which comprises compressingand cooling a. gaseous hydrocarbon mixture to liquefy higher molecularweight hydrocarbons and introducing the mixture into a first separatingzone, separately withdrawing liquids and gases from the said firstseparating zone, compressing and cooling the withdrawn gases andintroducing them into a second separating acne, passing the withdrawnliquids directly to said second separating zone, withdrawing liquids andgases separately from said second separating zone, passing the liquidswithdrawn from said I second separating zone to a fractionating zone,fractionating said liquids to obtain a normally liquid hydrocarbonfraction containing gasoline constituents and a vapor fractioncontaining C4 and lighter hydrocarbons, mixing'the gases and vapors fromsaid fractionating zone with the gases from said second separating zone,cooling the thus mixed gases and passing them to a third separating zoneto separate normally liquid hydrocarbons from gases, returning thenormally liquid hydrocarbons from said third separating zone to saidsecond separating zone, removing moisture from the gases from said thirdseparating zone, and compressing, cooling and fractionating theresulting dried gases to separate Ca, Ca and (24 fractions and anormally liquid fraction containing gasoline constituents.

2. A method of iractionating gaseous mixtures fractlonating zone,removing the overhead gaseous fraction, cooling said overheadgaseous'fraction to a temperature of about --50 F. and returning it tosaid fractionating zone as a reflux, removing overhead from saidfractionating zone a cold dilute ethylene gas fraction containing 8. Amethod according toclalm 7' wherein the ethylene and methane andremoving from the lower portion of said fractionating zone a. condensateliquid fraction containing C2 and higher hydrocarbons, each of saidfractions containing about half of the ethylene, reducing the pressureon the condensate liquid and fractionating it to separate a concentratedethylene gas fraction as an overhead fraction from a second condensateliquid containing C3 and higher hydrocarbons, reducing the pressure onthe second condensate and fractionating it to separate an. overheadfraction containing 03 hydrocarbons from a third liquid condensatecontaining C4 and higher hydrocarbons, reducing the pressure on thethird condensate and fractionating it to separate an overhead fractioncontaining C4 hydrocarbons from a final condensate liquid containinggasoline constituents.

3. A method according to claim 2 wherein reflux for said first twofractionating steps is provided by cooling the overhead gaseousfractions of the two steps with a refrigeration medium to condenseportions of said gaseous fraction and returning the thus condensedportions to the respective fractionation zones, and wherein the colddilute ethylene gas fraction from the first fractionation step is usedin part to cool the refrigeration medium.

4. A method according to claim 2 wherein driers used for drying thegaseous mixture become deactivatedand are reactivated with hot gas andthen cooied by using at least a portion of the colddiiu't'e ethylenefraction as a purging gas.

, Q QA method according to claim 2 wherein the cw' gaseous mixture isfirst cooled by indirect contact with a refrigerant to condense higherboiling constituents before the gaseous mixture is dried,

using a refrigerant for providing reflux for one. "of said fractionationsteps and then using the last mentioned refrigerant as the refrigerantfor cooling the gaseous mixture.

8. A method according to claim 2 wherein reflux for the first twofractionation steps is provided by cooling the overhead gaseousfractions of the said two steps with a refrigerating medium comprising aC3 hydrocarbon to condense portions of said gaseous fractions andreturning the time condensed portions to their respective fractionatingzones, and wherein at least a portion of the separated C3 fraction fromthe third fractionating step is added to the said refrigerating mediumto replace refrigerant lost during the process.

7. A method of separating lower molecular weight normally gaseoushydrocarbons from mixtures containing them which comprises compressingand cooling a gaseous hydrocarbon mixture to liquefy higher molecularweight hydrocarbons, separating liquids from gases in the cooled andcompressed charge, compressing and .cooling the separated gases andintroducing them gases and vapors with the gases from said separatingzone and cooling the mixture to condense normally liquid hydrocarbons,separating said normally liquid hydrocarbons from uncondensed gases, andreturning said normally liquid hydrocarbons to said separating zone.

10. A method of fractionating gaseousmixtures containing hydrocarbonswhich comprises drying the mixture, compressing and cooling the driedmixture and introducing it into a fractionating zone to remove anoverhead gaseous fraction, cooling said gaseous fraction to atemperature of about -50 F. and returning it to the said fractionatingzone as reflux, removing a cold dilute C2 fraction from a condensateliquid fraction containing higher hydrocarbons, each of said fractionscontaining about one half of the C3 hydrocarbons, reducing the pressure.on the condensate liquid and refractionating it to separate aconcentrated C2 overhead fraction from a second condensate liquidcontaining C3 and higher hydrocarbons, reducing the pressure on thesecond condensate and fractionating it to separate an overhead fractioncontaining 03 hydrocarbons from a third condensate liquid containing C4and higher hydrocarbons, reducingthe pressure on the third condensateand fractionating it to separate an overhead fraction containing C4hydrocarbons from a final condensate liquid containing gasolineconstituents.

11. A method according to claim 10 wherein driers used for drying thegaseous mixture become deactivated and are reactivated with hot gas andthen cooled by using at least a portion of the cold dilute C2 fractionas a purging gas.

12. A method according to claim 2 wherein the reflux for the first twofractionating steps .is provided by cooling the overhead fractions ofthe two steps with a refrigeration medium comprising a C3 hydrocarboncontaining an appreciable amount of ethane to condense portions of saidgaseous fractions, and returning the thus condensed portions to theirrespective fractionation zones.

13. A method of, fractionating gaseous mixture which comprisesfractionating a mixture containing ethylene, cooling the overheadgaseous fraction to a temperature of about -50 F., and returning thethus condensed portions to the fractionation zone as reflux wherebyabout halt of the ethylene is condensed in the fractionating zone, andremoving the remainder of the ethyl.-

ene in a stream comprising lower boiling constituents containing methaneand hydrogen.

14. A method of fractionating gaseous mixtures which comprisesintroducing a mixture containing ethylene into, a fractionating zone,maintaining a temperature of about 50 F. at the top of saidfractionating zone and removing a top fraction containing hydrogen,methane and about halt the ethylene and a bottom i'raction containingthe remainder of the ethylene in a the uncondensed gases consistingprincipally of hydrogen, methane and about half of the ethylene from theliquid condensate, adjusting-the temperature and pressure oi the liquidconden sate so iormed to vaporize the ethylene contained therein whileretaining the higher boiling constituents in liquid phase, separatingthe ethylene fraction so'vaporized from the remaining liquid condensate,thereafter further adjusting the temperature and pressure oi theremaining eondensate to vaporize another fraction therefrom separatingthe vaporized fraction from the unvaporized condensate, separatelycondensing the vaporized traction, and utilizing said last-namedfraction as a refrigerant in the cooling of said gaseous mixture.

16. A method of segregating gaseous hydrocarbon mixtures consistingpredominately oi oleilnic hydrocarbon gases obtained from the crackingof petroleum oils wherein the said gaseous hydrocarbon mixtures aresegregated into a. plurality of fractions oi diflerent'boiling range andmolecular weight which comprises compressin a substantially dry mixtureof said gases, cooling the compressed gases to a temperature suflicientto condense about half of the ethylene and the higher boilingconstituents of said gases under the obtaining pressure conditions butinsuflicient to condense constituents boiling below ethylene,

separating the uncondensecl gases consisting principally ofhydrogen,.methane and about half of the ethylene from the liquidcondensate, adlusting the temperature and pressure on the liquidoorniensatev so formed to vaporize the ethylene contained therein whileretaining the higher boiling constituents in liquid phase, separatingthe thylene fraction so vaporized from the remaining liquid condensate,and utilizing a portion of said last-named liquid condensate as arefrigerant (or cooling said gases.

BROOK I. SMITH, EDWARD G. MORIN'.

